1. Field of the Invention
This invention relates to a method of determining whether or not a conductor clamping section of a metal terminal is satisfactorily connected to a wire, and also relates to the metal terminal.
The present application is based on Japanese Patent Application No. Hei. 9-239567, which is incorporated herein by reference.
2. Description of the Related Art
A metal terminal includes an electrical contact section having a predetermined configuration, and a wire connecting section having a conductor clamping section which is connected to a wire by pressure contact. Before conducting the pressure contact, the wire is cut to a predetermined length, and then an insulating sheath at an end portion of the wire is removed.
When the metal terminal is connected to a conductor of the wire by pressure contact, the metal terminal must be completely electrically connected to the wire, and must have a holding force which is equivalent to the tensile strength of the wire. That is, the pressure contact of the metal terminal to the wire must be high both electrically and mechanically.
If the pressure contact is not sufficient, a gap may be formed between the conductor clamping section of the metal terminal and the conductor of the wire. In this case, since the holding force by the conductor clamping section is small, the conductor of the wire may easily come off the metal terminal.
A quality control test may be performed at the production site by cutting a conductor clamping section, which is clamping a conductor of a wire, of a metal terminal across the axis of the terminal. From the resultant section, the compressibility of the wire with respect to the conductor clamping section is calculated. Using the compressibility as one yardstick, the connection state between the metal terminal and the wire is determined.
On the other hand, when the metal terminal is connected to the wire by pressure contact, wire breakage preventing bellmouths are formed on both end portions of the conductor clamping section in an axial direction of the terminal so as to hem the end portions. Similar to the above-described quality control test, the width of the bellmouths in the axial direction of the terminal may be periodically measured in order to determine the formation state of the conductor clamping section.
In the above-described structure, it is troublesome to determine the connection state. That is, whenever the connection state between the metal terminal and the wire is to be determined, the conductor clamping section must be cut to examine the compressibility of the wire with respect to the conductor clamping section. Since the aforementioned operation takes a long time, manufacturing productivity is lowered.
Further, measurement of the dimensions of the bellmouths is troublesome because the bellmouths are extremely small. Therefore, such a measurement is liable to result in an error. Further, manufacturing productivity is lowered, and the connection of the wire is not sufficiently reliable.
In order to eliminate the above-described problems, it is an object of the present invention to provide a method of determining whether a metal terminal is satisfactorily connected to a wire, whether the wire is satisfactorily connected to a conductor clamping section of the metal terminal, and whether formation of wire breakage preventing bellmouths is acceptable, such that productivity and reliability of quality control may be markedly improved.
To achieve the above object, according to the first aspect of the present invention, there is provided a method of determining whether a metal terminal including a conductor clamping section for clamping a wire thereto is satisfactorily connected to the wire. First, a first metal terminal including a first conductor clamping section for clamping a first wire thereto is provided. Next, one of a dimensional variation and a ratio of a dimensional change of the first conductor clamping section in an axial direction of the first metal terminal, which are caused by clamping the first conductor clamping section, is calculated. Compressibility comparison data is then prepared by calculating, from a section of the first conductor clamping section after clamping the first conductor clamping section, compressibility of the first wire with respect to the first conductor clamping section based on the one of the dimensional variation and the ratio of the dimensional change. A second metal terminal including a second conductor clamping section for clamping a second wire is provided, it is determined whether the second metal terminal is satisfactorily connected to the second wire by comparing one of a dimensional variation and a ratio of a dimensional change of the second conductor clamping section with the compressibility comparison data. According to the first aspect of the present invention, after preparing the compressibility comparison data, for example, a dimensional variation or a ratio of a dimensional change of a conductor clamping section can easily be periodically calculated and compared with the compressibility comparison data. Accordingly, whether the conductor clamping section is satisfactorily connected to the wire or not can be readily determined. In addition, productivity and the reliability of quality control are markedly improved.
Further, according to the second aspect of the present invention, the method of the first aspect of the present invention further comprises a step of applying a connection state determining belt-shaped mark to each of the first conductor clamping section and the second conductor clamping section before clamping. In the calculating step, the one of the dimensional variation and the ratio of the dimensional change of the first conductor clamping section is calculated based on a change in width of the mark caused by clamping the first conductor clamping section. In the determining step, the one of the dimensional variation and the ratio of the dimensional change of the second conductor clamping section is compared with the compressibility comparison data. Therefore, if the width of the mark is constant, measurement of dimension about the calculation of the dimensional variation or the ratio of the dimensional change is simplified. That is, whether the conductor clamping section is satisfactorily connected to the wire or not can be more readily determined. Accordingly, productivity and quality control are markedly improved.
Further, according to the third aspect of the present invention, the method of the first aspect of the present invention further comprises a step of applying a pair of connection state determining belt-shaped marks to each of the first conductor clamping section and the second conductor clamping section before clamping, such that the belt-shaped marks are confronted with each other. In the calculating step, the one of the dimensional variation and the ratio of the dimensional change of the first conductor clamping section is calculated based on a change in distance between the marks caused by clamping the first conductor clamping section. In the determining step, the one of the dimensional variation and the ratio of the dimensional change of the second conductor clamping section is compared with the compressibility comparison data. Therefore, if the distance between the pair of the belt-shaped marks is constant, measurement of dimension about the calculation of the dimensional variation or the ratio of the dimensional change is simplified. That is, whether the conductor clamping section is satisfactorily connected to the wire or not can be more readily determined. Accordingly, productivity and quality control are markedly improved.
Further, according to the fourth aspect of the present invention, in the method of the third aspect of the present invention, the marks are respectively applied along formation reference positions of wire breakage preventing bellmouths. The bellmouths are formed on both end portions of each of the first conductor clamping section and the second conductor clamping section by clamping each of the first conductor clamping section and the second conductor clamping section. The method further comprises a step of determining whether the formation of the bellmouths is acceptable or not by comparing the respective marks with respective positions of the bellmouths. In addition to the effects of the third aspect of the present invention, the fourth aspect of the present invention provides an effect in that whether or not the formation of the bellmouth is acceptable can be determined.
Furthermore, according to the fifth aspect of the present invention, there is provided a terminal which comprises an electrically conductive plate including a conductor clamping section to which a wire is connectable, and at least one belt-shaped mark applied to the conductor clamping section. In the terminal, the belt-shaped mark is for determining whether the wire is satisfactorily connected to the terminal or not, after one of dimensional variation and a ratio of a dimensional change, caused by clamping the conductor clamping section, is calculated. Accordingly, if the dimensional variation or the ratio of the dimensional change in an axial direction of the terminal is calculated, and the compressibility comparison data is prepared, then whether or not the conductor clamping section is satisfactorily connected to the wire can be readily determined by comparing the dimensional variation or the ratio of the dimensional change of the mark with the compressibility comparison data. Accordingly, productivity and the reliability of quality control are markedly improved.
Further, according to the sixth aspect of the present invention, in the terminal of the fifth aspect of the present invention, a plurality of the belt-shaped marks are applied along formation reference positions of wire breakage preventing bellmouths which are formed on both end portions of the conductor clamping section after the conductor clamping section is clamped. Accordingly, whether the conductor clamping section is satisfactorily connected to the wire or not and whether the formation of the wire breakage preventing bellmouth is acceptable or not can be determined.
Further, according to the seventh aspect of the present invention, in the terminal of the sixth aspect of the present invention, the width of each of the marks is equal to a range of dimensional tolerance of each of the respective bellmouths. Accordingly, the formation of the bellmouth can be visually determined based on the position of the end of the bellmouth with respect to the mark after clamping the conductor clamping section.